To assess low and high power settings for the popcorn technique, and relationship of laser fiber-to-stone distance and calyceal size on submillimeter fragmentation. Our in-vitro findings may help guide strategies to improve a dusting technique for ureteroscopy.
BegoStones were fragmented in small (127 mm3) and large (411 mm3) sized bulbs to simulate calyces, using a 120W Ho:YAG laser. A 242μm fiber was introduced through a ureteroscope mounted to a 3D positioner with its tip located at 0 or 2 mm distance from the stones. 20W [1Jx20Hz, 0.5Jx40Hz] and 40W [1Jx40Hz, 0.5Jx80Hz] settings were assessed, including short pulse (SP) and long pulse (LP) modes. Total energy delivered was constant at 7.2KJ. Primary outcome was percentage of stone mass converted to fragments <1 mm. High-speed imaging was performed to study stone movement/fragmentation.
For all settings, popcorn lithotripsy yielded more submillimeter fragments when performed with the fiber positioned on the stone compared to 2 mm from the stone (p<0.05). Distribution of submillimeter fragments was higher when utilizing high frequencies regardless of pulse energy. At 2 mm distance, popcorning was more effective in the small model (p<0.05). At 2 mm distance, SP was superior to LP. Video analysis showed fragmentation did not occur when stones collided with each other. At 80Hz/2 mm distance, only 17.5% of pulses impacted fragments.
Popcorn technique is more effective when the fiber is directly in contact with stone, and when performed in a small calyceal model. Utilizing settings with higher frequencies may improve dusting outcomes.
Urology. 2018 Sep 05 [Epub ahead of print]
Ali H Aldoukhi, William W Roberts, Timothy L Hall, Joel M H Teichman, Khurshid R Ghani
Division of Endourology, Department of Urology, University of Michigan, Ann Arbor, MI. Electronic address: ., Division of Endourology, Department of Urology, University of Michigan, Ann Arbor, MI; Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI., Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI., Department of Urologic Sciences, University of British Columbia, Vancouver, British Columbia, Canada., Division of Endourology, Department of Urology, University of Michigan, Ann Arbor, MI.